c.1400, probably a fusion of Middle English scratten and crachen, both meaning "to scratch," both of uncertain origin. Related: Scratched; scratching. Billiards sense of "to hit the cue ball into a pocket" is first recorded 1909 (also, originally, itch), though earlier it meant "a lucky shot" (1850). Meaning "to withdraw (a horse) from a race" is 1865, from notion of scratching name off list of competitors; used in a non-sporting sense of "cancel a plan, etc." from 1680s. To scratch the surface "make only slight progress in penetrating or understanding" is from 1882. To scratch (one's) head as a gesture of perplexity is recorded from 1712.

1580s, "slight skin tear produced by a sharp thing," from scratch (v.). Meaning "mark or slight furrow in metal, etc." is from 1660s. American English slang sense of "money" is from 1914, of uncertain signification. Many figurative senses (such as up to scratch, originally "ready to meet one's opponent") are from sporting use for "line or mark drawn as a starting place," attested from 1778 (but the earliest use is figurative); meaning "nothing" (as in from scratch) is 1918, generalized from specific 19c. sporting sense of "starting point of a competitor who receives no odds in a handicap match." Sense in billiards is from 1850. Scratch-pad is attested from 1883.

in Old Scratch "the Devil," 1740, from earlier Scrat, from Old Norse skratte "goblin, wizard," a word which was used in late Old English to gloss "hermaphrodite;" probably originally "monster" (compare Old High German scraz, scrato "satyr, wood demon," German Schratt, Old High German screz "a goblin, imp, dwarf;" borrowed from Germanic into Slavic, as in Polish skrzat "a goblin").